Sometimes we as developers can be tempted to combine multiple conditional expressions in one long worm-like expression that is hard to understand, let alone test. Such cases should either be avoided or follow a coding style guide, which would at the very least improve the readability of a combined expression.

A simple description would say bad code equals untested or untestable code. While the former is something that can rather easily be overcome, the latter is a completely different story. It is unfortunately present in many legacy applications and takes a big amount of commitment and knowledge to overcome successfully.